(1) Field of the Invention
The present invention relates to a liquid crystal display device and a manufacturing method for the same, and in particular to a liquid crystal display device having gate wires and source/drain wires with a multilayer structure made of the same materials, as well as a manufacturing method for the same.
(2) Description of the Related Art
Liquid crystal display devices use thin film transistors TFT for driving display pixels. In addition, gate wires and source/drain wires are formed in a matrix in order to supply power to the thin film transistors. JP2008-311545A, for example, discloses gate wires formed of Mo or an alloy thereof, and source/drain wires formed of Al or an alloy thereof, and a layer of Ti or Mo that is provided on the top surface of Al or an alloy thereof.
In the case where gate wires and source/drain wires are formed of different materials, the difference in material causes the wires to have different electrical resistances. In order to solve this problem, it is necessary to adjust the thickness (film thickness) and width of the wires, but adjustment of the film thickness during the process makes the manufacturing steps extremely complex, and there is a limitation to how much the wires can be adjusted in width, due to the resolution of the mask.
Meanwhile, JP2002-72230A proposes a method for forming gate wires and source/drain wires with a multilayer structure of the same material. JP2002-72230A discloses wires made of multilayer films titanium, aluminum alloy and titanium nitride that have undergone a plasma etching process using a mixed gas of chlorine and argon.
In the case where gate wires and source/drain wires with a multilayer structure are formed of the same material, it is possible for the gate wires and the source/drain wires to have the same electrical resistance, and therefore there is an advantage, such that the patterning of wires having connections between the gate and source/drain wires is easy. It is necessary for the gate insulating film provided in a layer above the gate wires to have a high withstanding voltage, and therefore the coverage needs to be appropriate with the angle of the taper of the gate wires small. Meanwhile, it is necessary for the angle of the taper of the source/drain wires to be wide in order to increase the density of the wires, so that the frame of the liquid crystal display device can be made narrower.
Concerning the adjustment of the angle of the taper of wires, JP2002-72230A discloses the angle of the taper of wires, which is adjusted by adjusting the partial pressure of the argon gas. However, processing methods using dry etching, such as the plasma etching in JP2002-72230A, are more costly than those using wet etching, and have poor throughput, which makes continuous processing difficult and causes the cost of manufacture to increase.